The main problems with IMD to me are:
1) No standardized way of testing this. Different sources use different methods. S&R's methods make their results incomparable even with other speakers they've reviewed so it's very strange...
2) No research I've seen, or even anecdotal evidence, that IMD would be audible in cases where HD would not, with the exception of
a report from Harman about audible IMD+doppler distortion in older Kef 2-ways specifically. But you've already covered the doppler distortion issue(and thanks for doing those measurements, I haven't seen anybody else even attempt it).
Given these factors I haven't a clue how anybody is even supposed to interpret IMD to correlate with anything audible. It's hard enough with HD, which, as typically depicted, is already incredibly difficult to interpret in terms of correlation with audible problems.